Electric incandescent lamps



Nov. 30, 1965 w. J. M LINTIC 3,221,202

ELECTRIC INCANDESCENT LAMPS Filed Feb. 28. 1962 WiLLlAM JAMES ML|NTICINVENTOR.

ATTORNEY United States Patent 3,221,202 ELECTRIC INCANDESCENT LAMPSWilliam James McLintic, London, England, assignor to Thorn ElectricalIndustries Limited, London, England, a British company Filed Feb. 28,1962, Ser. No. 176,199 7 Claims. (Cl. 313-271) intervals where the wireis opened out or stretched out to be more or less straight. Thecontinuously wound filament is in some respects more convenient and moreeconomical, both in coiling and in the subsequent shaping or forming.

In the construction of a projection lamp with a continuously woundfilament a grid of closely-spaced parallel filament sections is formedby bending the filament into a zig-zag arrangement, for example withalternate sec tions lying behind and between the adjacent sections topresent a substantially unbroken illuminated area, this form being knownas the biplane construction. At each bend in the filament one turn ofthe coil forms a loop by means of which the grid is supported.

In use the filament is heated to a temperature near its melting pointand tends to unwind or twist to relieve strains set up during itswinding. Particularly at the ends of the filament, which are normallyrigidly fixed, this tends to cause distortion or squirming of thefilament sections and in view of the close spacing of the sections thissquirming produces a risk of short-circuiting of the end sections of thefilament and of the setting up of arcs.

It is an object of the present invention to provide a filament mountingwhich will substantially reduce squirmmg.

In accordance with the invention there is provided an electricincandescent lamp having a grid of closelyspaced filament sectionsformed from a single continuously-wound coil filament, in which the endsections of the grid are straight, the ends of the filament are in linewith the straight end sections, and the ends are plugged with a threadedplug, whereby twisting of the filament coil on heating is accommodatedby a screwing movement over the plug.

The threaded plug may be formed by a core wire overwound with finer wireto give the effect of a thread.

One embodiment of the invention will now be described by Way of example,with reference to the accompanying drawing, in which:

FIG. 1 is a general view of a projection lamp in accordance with theinvention, and

FIG. 2 is a detail of the filament and its mounting.

The lamp is of conventional form, having a generally cylindrical glassenvelope 10 mounted on a screw base 11. Within the envelope 10 a glasspress 12 supports pillars 13 and 14 of stout wire which serve assupports for the filament assembly and also as leads for conveyingcurrent to the filament. An upper insulating bar 15 is attached to thepillars 13 and 14 by brackets 16 and a lower insulating bar 17 isattached to the pillars 13 and 14 by brackets 18. The upper insulatingbar 15 supports a plurality of upper hooked supports 19 which are spacedapart and insulated from one another. The lower insulating bar 17similarly supports a plurality of lower hooked supports 20.

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The tungsten filament 21 consists of a single continuously-wound lengthbent into a zig-zag formation between the hooked supports 19 and 20(FIG. 2) with one turn of the coil forming a loop, such as 22, at eachbend for attachment to the hooked support. The filament sections 23extending between a lower and an upper hooked support are closelyspaced, with alternate sections lying behind and between the adjacentsections, in the known biplanar formation, so as to present asubstantially unbroken light source area.

The end filament sections 24 and 25 of the grid are straight and areparallel to and equal in length to the adjacent filament sections 23.The ends 26 and 27 of the filament 21 are in line with the straight endsections 24 and 25, respectively, of the grid and are mounted onthreaded plugs 28 and 29, respectively.

The threaded plug 28 is formed by a core wire 30 of refractory materialsuch as tungsten or molybdenum overwound with finer Wire 31 to give theeffect of a thread. It fills the Whole length of the end 26 of thefilament up to the beginning of the end filament section 24. The end 26of the filament 21 has been cut away in thedrawing to show theengagement of the turns of the filament with the turns of the threadformed by the fine wire 31.

The threaded plug 29 for the end 27 of the filament 21 is of similarconstruction.

The plugs 28 and 29 are bent outwards towards the pillars 13 and 14 at apoint beyond the ends 26 and 27 of the filament. They are thenspotwelded to pillars 13 and 14 respectively and serve for the supply ofcurrent to the filament 21.

When the filament is raised to its operating temperature it tends totwist to relieve residual strains resulting from its Winding. Thistwisting in the end sections of the grid is accommodated by a screwingmovement of the end of the filament over the threaded plug and the endsection of the filament is thus maintained straight, squirming beingavoided. Expansion of the coil due to rise in temperature facilitatesthis movement. To a lesser extent relief is also accorded to theinterior sections 23, which would otherwise be affected by movement ofsections 24 and 25 when these are rigidly fixed in the conventionalmanner.

In an alternative construction the end filament sections of the grid areinclined away from the adjacent sections but the plugged ends are stillkept in line with the respective end sections.

I claim:

1. An electric incandescent lamp comprising a base, a light-transmittingenvelope mounted on said base, support means disposed within saidenvelope, a single continuously-wound coil filament mounted on saidsupport means to form a grid of closely-spaced filament sections, saidgrid having straight end sections, all of said filament sectionsincluding said straight end sections being of equal length, and the endsof said filament having substantially the same pitch Winding as theadjoining end sections of the filament in line with said straight endsections, and a threaded plug forming part of said support means andplugging said ends of the filament, whereby twisting of the filamentcoil on heating is accommodated by a screwing movement over the plug.

2. A lamp as claimed in claim 1 in which the threaded plug is composedof a core wire overwound with finer wire to form the thread.

3. A lamp as claimed in claim 1 in which the end sections of the gridare inclined away from the adjacent filament sections.

4. A lamp as claimed in claim 1 in which the grid is of zig-zagformation, each pair of adjacent filament sections being joined by asingle turn of the filament forming a loop attaching the filament tosaid support means.

5. A lamp as claimed in claim 4 in which alternate filament sections liebehind and between the adjacent sections.

6. A lamp as claimed in claim 4 in which said support means includeupper and lower sets of hooked supports for said loops. 1

7. An electric incandescentlamp comprising a base, a sealedlight-transmitting envelope, conductive pillars mounted in said base andextehdirig within said envelope, upper and lower insulatingbai's'attached to and extending between said pillars, upper and lower sets ofhooked supports carried respectively by said upper and lower insulatingbars, a single continuously-wound filament ar,-

ranged to form a zig-zag grid of closely-spaced filament sections joinedby single turns of the filament engaged over said hooked supports, saidgrid having straight end, j

sections, all of said filament sections including said straigh endsections being of equal length, and the ends of said,

filament having substantially the same pitch winding as the adjoiningend sections of the filament in line with said straight end sections,and a threaded plug in electrically-conductive attachment with saidpillars plugging said ends of the filament, whereby said filament canturn without squirming on said plug when heated during operation of thelamp.

References Cited by the Examiner UNITED STATES PATENTS 1,292,482 1/1919Keyes 313-315 2,134,574 10/1938 Pinkle 313315 2,404,992 7/ 1946 Stone313271 2,449,679 9/ 1948 Van Horn 313271 2,523,033 9/1950 Leighton 3l3278 5 2,605,440 7/1952 Gero 4 313273 X 2,950,413 8/1960 Jayneet a1313-113 X DAVID J. Primary Examiner.

JJIIAMES D. Examiner.

1. AN ELECTRIC INCANDESCENT LAMP COMPRISING A BASE, A LIGHT-TRANSMITTINGENVELOPE MOUNTED ON SAID BASE, SUPPORT MEANS DISPOSED WITHIN SAIDENVELOPE, A SINGLE CONTINUOUSLY-WOUND COIL FILAMENT MOUNTED ON SAIDSUPPORT MEANS TO FORM A GRID OF CLOSELY-SPACED FILAMENT SECTIONS, SAIDGRID HAVING STRAIGHT END SECTIONS, ALL OF SAID FILAMENT SECTIONSINCLUDING SAID STRAIGHT END SECTIONS BEING OF EQUAL LENGTH, AND THE ENDSOF SAID FILAMENT HAVING SUBSTANTIALLY THE SAME PITCH WINDING AS THEADJOINING END SECTIONS OF THE FILAMENT IN LINE WITH SAID STRAIGHT ENDSECTIONS, AND A THREADED PLUG FORMING PART OF SAID SUPPORT MEANS AND